[mongoose] add unwind method with new params type

In mongodb 3.2, the unwind operator can with a object params.

mongoose/index.d.ts

@@ -2163,6 +2163,11 @@ declare module "mongoose" {
      * @param fields the field(s) to unwind
      */
     unwind(...fields: string[]): this;
+    /**
+     * Appends new custom $unwind operator(s) to this aggregate pipeline
+     * new in mongodb 3.2
+     */
+    unwind(...opts: { path: string, includeArrayIndex?: string, preserveNullAndEmptyArrays?: boolean }[]): this;
   }
 
   /*